Some years ago I noticed that the (steel) screw that held the ground lug for
the B+ bypass
capacitor in a relatively low-powered (single 813) amplifier appeared to have
oxidized.
This screw was close to the tank circuit and I suspect that it had heated up
from the
induced currents. I've seen warnings in the literature about using ferrous
hardware in
strong RF fields, too.
I use brass screws where I think there will be an RF field, although I do use
steel ones
in the power supply sections, etc. After all, a little more iron in that part
of the
amplifier shouldn't matter!
On 11/19/2010 7:50 AM, Fuqua, Bill L wrote:
> Inductive ovens operate at low frequencies, 100kHz and less usually. That is
> to get a greater skin depth.
> Due to skin effect, if you are operating in the MHz range most of the current
> will be thru the plateing not the core material.
> Most plateings have high resistivity and are thick as well and some have two
> layers to allow a good bond between the
> final plate and the core material.
> 73
> Bill wa4lav
>
> ________________________________________
> From: amps-bounces@contesting.com [amps-bounces@contesting.com] On Behalf Of
> DJ7WW [dj7ww@t-online.de]
> Sent: Friday, November 19, 2010 5:56 AM
> To: amps@contesting.com
> Subject: Re: [Amps] Plated screws
>
> You will find out quickly if you use them to connect copper straps to coils
> or band switches or elsewhere in rf fields.
>
> In inductive ovens the same "eddy current" works quite effective
>
> 73
> Peter
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of n8de@thepoint.net
> Sent: Freitag, 19. November 2010 06:15
> To: Stirling Schmidt
> Cc: AMPS submit
> Subject: Re: [Amps] Plated screws
>
> Please explain WHY magnetic screws are 'inappropriate' for amp building?
>
> 73
> Don
> N8DE
>
>
>
> Quoting Stirling Schmidt<kc0nxm@sbcglobal.net>:
>
>> Hi all:
>> Where's a good place to source nickel-plated brass screws? I have
>> some from ages
>> ago, but I'm assuming the hardware store zinc-steel variety are
> inappropriate
>> for amp assembly, as they are magnetic.
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>
>
>
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--
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/
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